(R)-3-[2-(2-Hydroxymethylpyrrolidin-1-yl)ethyl]-5-methyl-2H-isoquinolin-1-one and hydrochloride dihydrate thereof is a compound described in Example 36 of WO 2004/031171 (patent document 1). This compound possesses a potent poly(ADP-ribose)polymerase (Poly(ADP-ribose)polymerase; hereinafter to be abbreviated as “PARP”) inhibitory action, and is useful for the treatment or prophylaxis of cerebral infarction.
While a free form and hydrochloride dihydrate of the aforementioned compound are described in Example 36 of patent document 1, other salt forms are not specifically described.    patent document 1: WO 2004/031171